Discharge lamp with capacitive socket

ABSTRACT

The discharge lamp has a discharge vessel (10) and a socket (20) made of an electrically insulating material. Two electrodes (12, 13) project into the discharge vessel (10), with which electrical lines (16,17) are connected, which are conducted through the socket (20). A first electrically conductive component (22) is connected with the one line (16), and a second electrically conductive component (26) is connected with the other line (17), surrounds the first component (22) and is separated from it by the insulating material of the socket (20). The two components (22, 26), together with the insulating material of the socket (20), constitute a capacitive component, which is switched in parallel between the two lines (16,17), thus preventing or at least reducing the spreading of electromagnetic interference along the lines (16,17).

BACKGROUND OF THE INVENTION

The invention relates to a discharge lamp, in particular for vehiclelighting systems.

Such a discharge lamp is known from DE 36 03 743 A1. This discharge lamphas a discharge vessel with two electrodes arranged inside. In addition,the discharge lamp has a socket made of electrically insulatingmaterial, through which electrical lines are conducted to theelectrodes. Discharge lamps are commonly operated at high voltage and ithas been shown that electromagnetic interference along the electricallines to the lamp tends to occur during operation. In DE 43 10 307 it issuggested to place a filter circuit into a housing near the dischargelamp in order to prevent or at least reduce the spreading ofelectromagnetic interference. The filter circuit has a condenser amongother things, which is connected in parallel with the electrical linesto the discharge lamp. However, this additional filter circuitrepresents a large expenditure and creates additional costs.

ADVANTAGES OF THE INVENTION

In contrast thereto, the discharge lamp in accordance with the inventionhas the advantage that with the addition of a few components acapacitively acting component is integrated into the socket of thedischarge lamp, by means of which the spreading of electromagneticinterference via the electrical lines to the lamp is prevented or atleast reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is shown in the drawings and ismore closely explained in the following description.

FIG. 1 shows a discharge lamp in cross-section.

FIG. 2 shows the discharge lamp in cross-section along line II--II inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A discharge lamp for vehicle lighting systems, in particular for motorvehicle head lights as shown in FIGS. 1 and 2, has a discharge vessel 10with two inward extending electrodes 12 and 13. In the exemplaryembodiment shown, the electrodes 12, 13 are arranged opposite each otherin the direction of the longitudinal axis 14 of the lamp. However, it isalso possible to arrange the electrodes in such a way that they aresituated opposite each other transversely to the longitudinal axis 14 ofthe lamp. The discharge vessel 10 contains a mixture of differentsubstances which, when a voltage is applied between the electrodes 12,13, are excited to output light. Preferably the discharge vessel 10contains mercury under high pressure and, if desired, a metal halide, ora mixture of different metal halides. In addition, the discharge vesselcan contain a rare gas, for example xenon.

An electrical line 16 or 17 which leads to a socket 20 of the dischargelamp is connected to each electrode 12, 13. The line 16 connected to theelectrode 12 leading to the socket 20 is disposed approximatelycentrally in respect to the discharge vessel 10 and approximatelyparallel with the longitudinal axis 14 of the lamp, and the line 17connected to the other electrode 13 is disposed off center andapproximately parallel with the longitudinal axis 14 of the lamp. Thesocket 20 of the discharge lamp is made of an electrically insulatingmaterial, for example a plastic or ceramic material. A component 22 madeof an electrically conductive material is connected with the end of theline 16 arranged in the socket 20, which for example is embodied as asleeve which is round at least on its exterior, and which is disposedcoaxially with the longitudinal axis 14 of the lamp. The component 22 isenveloped by the insulating material of the socket 20, at least at itsexterior circumference. In the direction of the longitudinal axis 14,the component 22 has a length 1 and a radius of rl in relation to thelongitudinal axis 14.

A component 26 made of an electrically conductive material is alsoconnected with the end of the other line 17 arranged in the socket 20.The socket 20 has a widening 21 in which the end of the line 17 has beenplaced. The component 26 is essentially embodied in a ring shape and hasa connecting piece 27, by which it is connected to the end of the line17, and a ring-shaped section 28, which envelops the component 22. Thering-shaped section 28 of the component 26 is preferably disposedcoaxially with the component 22 and thus with the longitudinal axis 14,so that the distance between the exterior circumference of the component22 and the interior circumference of the section 28 is constant. Viewedin the direction of the longitudinal axis 14 of the lamp, thering-shaped section 28 of the component 26 is disposed in the same areaas the component 22 and preferably extends over the same length 1 as thecomponent 22. Thus, viewed in the direction of the longitudinal axis 14of the lamp, the ring-shaped section 28 of the component 26 is disposedat least almost congruently with the component 22. The ring-shapedsection 28 of the component 26 is disposed on a radius r2 around thelongitudinal axis 14, and embodied to be closed over its entirecircumference, but can also be designed with breaks. At its end pointingaway from the discharge vessel 10, the ring shaped section 28 of thecomponent 26 has an edge 29 projecting radially outward in respect tothe longitudinal axis 14. The component 26 is almost completelyenveloped by the insulating material of the socket 20. In its areadisposed outside the socket 20 in the direction toward the electrode 13,the line 17 can be provided with an electrically insulating sheath 30.

The components 22 and 26 are preferably made of metal, for examplecopper, and are electrically separated from each other by the insulatingmaterial of the socket 20 between them. During the operation of thedischarge lamp, the components 22 and 26 generate a capacitive effect bymeans of the insulating material of the socket 20 and form a capacitivecomponent, which is connected in parallel between the two lines 16 and17. The capacitance C of this component can be determined in accordancewith the following equation: ##EQU1## Wherein: ε_(r) is the dielectricconstant of the insulating material of the socket,

ε₀ is the electrical field constant, which is 8.854 10-12 F/m,

r1 is the radius of the interior component 22,

r2 is the radius of the ring shaped section 28 of the exterior 26,

l is the length of components 22, 28.

By respective variations of the measurement l and/or r1 and/or r2, acapacitive component of preset capacitance can be formed. Particularlythrough variation of the length 1, the capacitance can easily bechanged. Usable materials for the socket 20 of the discharge lamp canfor example be polyether imide, PEI, which has a dielectric constantε_(r) of approximately 3.5. At values r1=4 mm and r2=5.2 mm, acapacitance of approximately 5.9 pF results with the length 1 being 8mm, with the length 1 being 10 mm, a capacitance of 7.4 pF will result,with the length 1 being 12 mm, a capacitance of 8.9 will result. Anotherusable material for the socket 20 can also be polyphenylene sulfide,PPS.

Connecting elements arranged on the side of the socket 20 which isopposite from the discharge vessel 10 are connected with the lines 16,17. For example, a plug sleeve 31 or a pin plug can be connected withthe centrally located line 16, and a conductor ring 32 with the offcenter line 17. A plug component, not shown, which has correspondingcounter connecting elements, can be attached on the socket 20 of thedischarge lamp.

The socket 20 of the discharge lamp is preferably produced by injectionmolding, wherein the components 22, 26 are placed in predetermined orderto each other into an injection mold, and are covered with theelectrically insulating plastic material of the socket.

In place of the aforementioned ring-shaped embodiment of components 22and 26, a plate-shaped embodiment of these components is also possible.In this case a plate-shaped electrical conductive component is alsoconnected with each line 16, 17, wherein the two components areseparated from each other by the insulating material of the socket 20and form a plate capacitor.

We claim:
 1. A discharge lamp for vehicle lighting systems, comprising adischarge vessel; at least two electrodes extending into said dischargevessel; a socket composed of an electric insulating material; electricallines conducted to said electrodes through said socket; at least twocomponents composed of electrically conductive material and disposed insaid socket, said components being connected with said electrical lines,said components assigned to said electrical lines being electricallyseparated from each other by said insulating material of said socket,and together with said insulating material of said socket constituting acapacitive component.
 2. A discharge lamp as defined in claim 1, whereinsaid socket is composed of plastic.
 3. A discharge lamp as defined inclaim 2, wherein said socket is composed of polyetherimide.
 4. Adischarge lamp as defined in claim 2, wherein said socket is composed ofpolyphenylene sulfide.
 5. A discharge lamp for vehicle lighting systems,comprising a discharge vessel; at least two electrodes extending intosaid discharge vessel; a socket composed of an electric insulatingmaterial; electrical lines conducted to said electrodes through saidsocket; at least two components composed of electrically conductivematerial and disposed in said socket, said components being connectedwith said electrical lines, said components assigned to said electricallines being electrically separated from each other by said insulatingmaterial of said socket, and together with said insulating material ofsaid socket constituting a capacitive component, a first one of saidcomponents being connected with one of said lines and having a somewhatcylindrically shaped exterior, a second one of said components beingconnected with another of said lines and having an approximatelyring-shaped section which surrounds said first component at a distance.6. A discharge lamp as defined in claim 5, wherein said first componentand said ring-shaped section of said second component are disposed atleast coaxially.
 7. A discharge lamp as defined in claim 5, wherein oneof said electrodes and one of said lines connected with said oneelectrode are arranged approximately centrally in respect to alongitudinal axis of the lamp, said first component being connected withsaid one line, another of said electrodes and another of said linesconnected with another of said electrodes being arranged off center inrespect to the longitudinal axis of the lamp, said second componentbeing connected with said another line.
 8. A discharge lamp as definedin claim 5, wherein said components are arranged at least approximatelycongruently in a direction of a longitudinal axis of the lamp.
 9. Adischarge lamp for vehicle lighting systems, comprising a dischargevessel; at least two electrodes extending into said discharge vessel; asocket composed of an electric insulating material; electrical linesconducted to said electrodes through said socket; at least twocomponents composed of electrically conductive material and disposed insaid socket, said components being connected with said electrical lines,said components assigned to said electrical lines being at leastpartially enveloped by said insulating material of said socket andelectrically separated from each other by said insulating material ofsaid socket, and together with said insulating material of said socketconstituting a capacitive component which prevents or at least reduces aspreading of electromagnetic interference via said electrical lines tothe lamp.